1. Field of the Invention
The present invention relates to a magnetic sensor using Hall elements, and to a method of manufacturing the magnetic sensor, in particular, to a magnetic sensor having a magnetic flux converging plate, and is configured to detect vertical and horizontal magnetic fields, and to a method of manufacturing the magnetic sensor.
2. Description of the Related Art
Hall elements are used in various applications since non-contact position detection and non-contact angle detection can be made by Hall elements as magnetic sensors.
First, the principle of magnetic detection with the Hall elements is described. When a magnetic field is applied vertically to a current flowing through a substance, an electric field (Hall voltage) is generated in a direction vertical to both the current and the magnetic field. Typical Hall elements are thus configured to detect a vertical magnetic field component with a current caused to flow on a surface of a substrate or a wafer made of silicon or other material.
In addition, it is known that the Hall elements can detect not only a vertical magnetic field but also a horizontal magnetic field in combination with a magnetic thin film made of a material having high magnetic permeability, with use of the magnetic thin film as a magnetic flux converging plate configured to change a direction of a magnetic flux to guide the magnetic flux to the Hall elements (see, for example, Japanese Patent Application Laid-open No. 2002-071381).
The magnetic sensor including the magnetic flux converging plate may be manufactured as follows. For example, the Hall elements are formed on the silicon substrate, and then the magnetic flux converging plate is formed on the silicon substrate by electroplating. Alternatively, a protective film made of polyimide or other materials is formed on a front surface of the silicon substrate, and the magnetic flux converging plate is formed on the protective film by electroplating (for example, see WO 07/119569 A1).
When the magnetic flux converging plate is formed on the silicon substrate having the Hall elements formed thereon, large stress is generated on the silicon substrate because the thermal expansion coefficients of a metal magnetic body and the silicon substrate or the protective film made of polyimide or other materials are significantly different from each other. The stress affects the magnetic sensor, increasing shift or fluctuations in the magnetic characteristics.